1. Field of the Invention
The present invention relates to an electric circuit board module for mounting various kinds of electric components such as resistors, capacitors, integrated circuit (IC) devices, hybrid IC devices, and substrates on an electric circuit board and, more particularly, to a multi-layer circuit board including plural electric circuits with those electric components mounted thereon.
2. Description of the Prior Art
Conventionally, electric components such as registers, capacitors, IC devices, hybrid IC devices, and substrates are mounted on the electric circuit board mainly by one of the following two methods. The first method is a flow soldering in which the electric circuit board substrate with electric components adhered at the predetermined position thereof is moved over a flowing wave of molten solder to solder the electronic components. The second method is a reflow soldering in which the heat is applied to the electric circuit board substrate, which is coated with a soldering paste at the predetermined positions and has electric components mounted thereon, to form a joint by reflowing the solder.
As demands for the down-sizing and cost reduction of the electronic devices, the high integration of the electric components mounted on an electric circuit board has become increasingly important, resulting in the smaller electric components and the electric circuit board with electrodes at a fine pitch such as 150 .mu.m. However, the previous two methods have soldering errors such as a short circuit caused by a solder bridge and an incomplete joint caused by a solder ball, when applied for soldering such smaller electric components on the electric circuit board with fine pitch electrode.
Especially in the reflow soldering, since the soldering paste easily degrades due to oxidization of the metallic components included therein, it is difficult to obtain the fine soldering paste good for printing on such fine-pitch-electrode circuit boards. Furthermore, both in the flow and reflow soldering methods, since the soldering paste shall be heated up to a high temperature for making molten solder, electric components joined by the soldering are affected significantly by the heat, causing the degradation of the electric components. The joints between electric components and the circuit board are unreliable.